A conventional biological information monitoring system, which is provided with a laser blood flow meter for measuring a blood velocity of a subject, is disclosed in Patent Document 1. More specifically, the biological information monitoring system is provided with the laser blood flow meter, which measures a blood velocity based on a scattering beam caused by a laser beam that is emitted into a body tissue and then scattered within the body tissue.
More specifically, this laser blood flow meter is provided with a receiving case, which receives therein a beam emitting device for emitting a laser beam into a body tissue, a detection device for detecting a scattering beam caused by the laser beam that is emitted by the beam emitting device and then scattered within the body tissue, and a beam condensing device for condensing the above-mentioned scattering beam and enabling the above-mentioned detection device to detect it, wherein a contact surface, which is a part of an outer peripheral surface of the receiving case and comes into contact with a surface of the body tissue when making measurement, is substantially flat.    Patent Document 1: Publication of Japanese Patent No. 3490433